Spin-photon systems for scalable quantum processors

Optical technologies are key to many communications, measurement and sensing tasks. In fact optical communication (in low loss fibres) underpins the global economy, supporting the near instantaneous transmission of terabits of information worldwide. However all-optical switching and computing have not developed dramatically despite optimism in the 1990's. This is primarily because of the problem of weak optical nonlinearity leading to high power requirements and low switching speeds. In this proposal I will develop a new optical switching technology based on the coupling of atom like defects in solid state hosts. The technology promises a high speed low power optical switch which could revolutionise all optical networks with routing and many other signal conditioning tasks performed in the all-optical domain.

The more recent developments of quantum photonic technologies such as quantum secured key distribution and the vision of quantum computing are also limited by the lack of a non-linearity at the single photon level. The missing component is in fact a deterministic entangler capable of inducing strong correlations between separate photons or between separate solid state realisations of quantum bits. This project aims to develop such gates based on our earlier invention a spin photon entangler which uses a singly charged quantum dot or colour centre strongly coupled to a microcavity. It turns out this element is a universal gate for quantum computation and experimental realisation of this gate is a key target here. Once such a component is available it will pave the way to a long range 'quantum internet' and to the development of a scalable quantum computer technology allowing both circuit and measurement based quantum computing realisations to be envisaged.

The end goal is to develop a technology that addresses both classical and quantum applications using single atom-like light emitters embedded in wavelength scale optical cavities (or waveguides) configured as either attojoule optical switches or high-fidelity efficient spin-photon entangling gates.

Photonics technologies underlie the transfer of many terabits per second of information across the globe and are key to the global digital economy enabling trillions of dollars of online business to be carried out each day. The development of a switching technology operating at energy levels orders of magnitude below present capabilities at orders of magnitude faster switching speeds will have dramatic impact on the architecture and power consumption of future all optical networks. The long-term potential impact of the quantum technologies themselves could be immense, opening up a whole new branch of technology promising unprecedented sensing sensitivity, measurement accuracy, computational potential and quantum secured internet as well as many yet to be discovered applications. Its potential has been recognised by the government's decision to invest £270 million in quantum technologies over the next 5 years. The PI is heavily involved in hub bids for quantum imaging and quantum communications and will thus actively feed out results to these or the successful hubs when announced. This proposal targets two primary bottlenecks of optical quantum technology, providing potential solutions to both the quantum memory requirement and a deterministic gate technology. Success of this project will thus ensure that the UK is a world leader in the development and application of this new and emerging science and technology. I will continue to identify and write up key commercial patents as they arise within the project and actively engage with companies to develop this technology. We have established links with major players including E6, Toshiba and Nokia and Bristol start-ups Qumet and Venture photonics. To guide the switch development we will actively engage with communications systems engineers, noting the recent addition of a high performance a quantum networks group in Bristol. I will meet regularly with our collaborators face to face and online. In addition, I will organise a Quantum Switching Workshop in the 3rd year of the fellowship involving collaborators, world leading groups and industry to guide future developments. The fellowship will develop strong links with the newly funded Bristol Quantum Engineering Centre for Doctoral Training helping to develop the next generation of researchers. The primary form of written dissemination will be through publication in the best journals in engineering, physics, photonics and Nanoscience accompanied by timely presentations at major conferences and wider engagement of the general public through outreach activities both live and on-line.